# Convert string to base64 string
function ConvertTo-Base64String([string]$string)
{
    $byteArray = [System.Text.UnicodeEncoding]::Unicode.GetBytes($string)
    [Convert]::ToBase64String( $byteArray )
}
 
# Convert base64 string to string
function ConvertFrom-Base64String([string]$string)
{
    $byteArray = [Convert]::FromBase64String($string)
    [System.Text.UnicodeEncoding]::Unicode.GetString($byteArray)
}
 
# test case
$wishWords = 'VINel9SCXXlQAG8AdwBlAHIAUwBoAGUAbABsAKR/y1PsThr/sGV0XutfUE4M/2yaMFIQYp9SDP9smnReJ1kJVAz/aFG2W3hej3kB/wH/Af8='
$wishWords = ConvertFrom-Base64String $wishWords
 
for($i=1;$i -le $wishWords.Length;$i++)
{
    Clear-Host
    $wishWords.Substring(0,$i)
    sleep -Milliseconds 200
}